In the natural world, DNA provides a kind of blueprint that directs a complex molecular dance which culminates in the creation of a much larger, more complex object 鈥� be it bacterium or elephant.
Now, using a method known as 鈥�DNA origami鈥�, chemists have managed a similar if much simplified version, creating artificial DNA that can also build itself into larger, more complex structures.
DNA with those capabilities could provide new ways of manufacturing on a small scale 鈥� for example, in the field of nanoelectronics 鈥� or performing calculations.
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The new method has been developed by and , both at the California Institute of Technology in Pasadena.
Snowball effect
Rothemund showed in 2006 how mixing a single, long DNA with many smaller strands could create a 2D 鈥渃anvas鈥�, 100 nanometres across, that could display patterns such as a map of the Americas.
Now the researchers have shown that such canvases can behave like programmable 鈥渟eeds鈥� 鈥� smaller DNA tiles attach to the seed and the structure snowballs in size to make a structure up to 100 times bigger than the original segment.
To make that happen, the team created two kinds of artificial DNA molecule 鈥� a long sequence that folds into the flat 鈥渟eed鈥� and a number of short sequences that each fold into smaller tiles.
When the two unwound types of DNA undergo cycles of temperature variation between 40 and 90 掳C, they fold into seeds and tiles, and then begin to accrete together into the much larger structure. The 鈥済rowth鈥� process is directed by the sequence of information written into the seed鈥檚 DNA.
That seed information coordinates which tiles attach on the first layer of tiles, explains Winfree. The sequences that make up that first layer then carry the information that directs the formation of the next layer of tiles, and so on.
Chinese whispers
A seed can build a coat for itself out of different types of tiles arranged into a regular pattern. That pattern is then repeated, as the first tile layer coordinates the formation of the second layer into a scaled-up mirror of the original one.
As well as simply scaling up a pattern, sequences can have 鈥渃ounting programs鈥� built into their code that makes it possible for a seed to specify a particular pattern or arrangement after a given number of layers.
鈥淚t鈥檚 sort of like the [also known as Chinese whispers],鈥� says Winfree.
Anyone that has played that game will know that it doesn鈥檛 take long for the original message to become distorted. To prevent that, he says, the team has designed the tile DNA sequences to 鈥減roof read鈥� their own work and spontaneously reject most erroneous assembly steps.
Universal machine
Although the team has so far used the technique to build simple pipes (see image, top right), much more is possible, Winfree says. 鈥淢etaphorically, this is similar to how genetic programs within cells direct the growth of an organism.鈥�
Winfree and Rothemund speculate that the technique could provide a way to assemble molecular components into useful structures such as tiny electric circuits. It is also possible to use the self-assembling DNA structures to perform computational tasks, adds Winfree.
鈥淚t is very powerful for information processing,鈥� he says. 鈥淚t鈥檚 what鈥檚 known as a , which means it can carry out any information processing task.鈥�
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